Modified Vanadium Oxide Catalysts for the Selective Catalytic Reduction of NOx
Doctoral thesis, 2025
Combustion processes in diesel engines are expected to play a significant role in the foreseeable future, especially in heavy-duty vehicles. In response to increasingly stringent legislations aimed at reducing emissions of nitrogen oxides (NOx), considerable efforts have been devoted to developing effective technologies to reduce NOx emissions. Among them, the selective catalytic reduction (SCR) with ammonia (NH3) is the most established method for both stationary and mobile sources.
To date, titania-supported vanadium oxides (VOx/TiO2) are the most widespread SCR catalyst type in use. However, the application in vehicles presents several challenges due to the dynamic conditions. Both low-temperature activity and high-temperature stability are crucial due to temperature fluctuations in the exhaust gas. Catalyst development has focused on enhancing activity by modification of the active VOx species and the support.
In this work, the effects of the vanadium loading and catalyst modification were investigated, with a particular emphasis on the behavior after thermal stress, representing a critical factor in the context of mobile source applications. Promising results have been achieved through the modification with oxides of cerium (Ce), niobium (Nb), and antimony (Sb), demonstrating the optimization potential of V-based SCR catalysts. The results showed that the Ce-modification results in an improved low-temperature activity, while the incorporation of Nb contributes to a higher thermal stability. Remarkable catalyst activation was observed after aging upon Sb-modification. The addition of modifiers enhanced the stability by limiting sintering processes of both the TiO2 and VOx species. Infrared spectroscopic methods allowed the identification of surface VOx species, surface hydroxyl groups, and adsorbed surface species of the reactants and products (NH3, NO, H2O). Further, the decomposition of the NO adsorption spectra enabled a comparison of the surface species ratio among the samples and provide potential for future in-depth spectroscopic studies. This thesis encourages further exploration of VOx/TiO2 catalysts to improve fundamental knowledge about catalyst design in the NOx emission control and beyond other applications.
To date, titania-supported vanadium oxides (VOx/TiO2) are the most widespread SCR catalyst type in use. However, the application in vehicles presents several challenges due to the dynamic conditions. Both low-temperature activity and high-temperature stability are crucial due to temperature fluctuations in the exhaust gas. Catalyst development has focused on enhancing activity by modification of the active VOx species and the support.
In this work, the effects of the vanadium loading and catalyst modification were investigated, with a particular emphasis on the behavior after thermal stress, representing a critical factor in the context of mobile source applications. Promising results have been achieved through the modification with oxides of cerium (Ce), niobium (Nb), and antimony (Sb), demonstrating the optimization potential of V-based SCR catalysts. The results showed that the Ce-modification results in an improved low-temperature activity, while the incorporation of Nb contributes to a higher thermal stability. Remarkable catalyst activation was observed after aging upon Sb-modification. The addition of modifiers enhanced the stability by limiting sintering processes of both the TiO2 and VOx species. Infrared spectroscopic methods allowed the identification of surface VOx species, surface hydroxyl groups, and adsorbed surface species of the reactants and products (NH3, NO, H2O). Further, the decomposition of the NO adsorption spectra enabled a comparison of the surface species ratio among the samples and provide potential for future in-depth spectroscopic studies. This thesis encourages further exploration of VOx/TiO2 catalysts to improve fundamental knowledge about catalyst design in the NOx emission control and beyond other applications.
aging
NOx emission control
VOx
Nb
vanadium oxide
Sb
NH3-SCR
titania
Ce
KB-salen, Kemigården 4, Chalmers.
Opponent: Dr. Davide Ferri, Paul Scherrer Institute (PSI), ETH Zurich, Switzerland.
Author
Alexander Nellessen
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Antimony modification of VOx/TiO2 NH3-SCR catalysts and the effect of thermal aging
Journal of Catalysis,;Vol. 450(2025)
Journal article
Impact of Vanadium Loading and Thermal Aging on the Surface Properties of Titania-Supported Vanadium Oxide
Journal of Physical Chemistry C,;Vol. 128(2024)p. 2894-2908
Journal article
Cars are bad for the environment, right?
Sure, but why? — Primarily because they release various pollutants upon the combustion of fuel. Among them, nitrogen oxide gases (NOx) are one of the most critical, contributing to smog and damaging our lungs, and top target for clean air regulations worldwide. Especially diesel-engine powered vehicles produce a lot of NOx. Although electric vehicles are on the rise, we’ll still be relying on diesel-powered vehicles, especially in heavy-duty vehicles such as trucks and buses.
The solution? — With the help of catalysis, NOx gases can be transferred into harmless nitrogen and water. This process is called Selective Catalytic Reduction (SCR). It sounds easy on paper, but is tricky in practice, where the catalysts face a harsh environment in vehicles: the exhaust temperatures constantly go up and down, so the catalyst must work both at low and high temperatures but also last for years.
The challenge is clear — the design of efficient and durable catalysts. In this work, we want to understand the impact of the long-term application on these catalysts by performing an accelerated aging protocol. We also tested ways to make these catalysts better by modification by adding other metal oxides. These additives helped to improve the catalyst’s stability and kept it active. Using infrared spectroscopy, we studied the catalyst’s surface to improve fundamental understanding. This work clarifies catalyst design principles and provides potential for upcoming studies.
Sure, but why? — Primarily because they release various pollutants upon the combustion of fuel. Among them, nitrogen oxide gases (NOx) are one of the most critical, contributing to smog and damaging our lungs, and top target for clean air regulations worldwide. Especially diesel-engine powered vehicles produce a lot of NOx. Although electric vehicles are on the rise, we’ll still be relying on diesel-powered vehicles, especially in heavy-duty vehicles such as trucks and buses.
The solution? — With the help of catalysis, NOx gases can be transferred into harmless nitrogen and water. This process is called Selective Catalytic Reduction (SCR). It sounds easy on paper, but is tricky in practice, where the catalysts face a harsh environment in vehicles: the exhaust temperatures constantly go up and down, so the catalyst must work both at low and high temperatures but also last for years.
The challenge is clear — the design of efficient and durable catalysts. In this work, we want to understand the impact of the long-term application on these catalysts by performing an accelerated aging protocol. We also tested ways to make these catalysts better by modification by adding other metal oxides. These additives helped to improve the catalyst’s stability and kept it active. Using infrared spectroscopy, we studied the catalyst’s surface to improve fundamental understanding. This work clarifies catalyst design principles and provides potential for upcoming studies.
KCK - Kompetenscentrum Katalys 2022-2026
Umicore Denmark ApS (KCK2022-2026), 2022-01-01 -- 2026-12-31.
Scania AB (Dnr:2021-036543Pnr:52689-1), 2022-01-01 -- 2026-12-31.
Preem (KCK2022-2026), 2022-01-01 -- 2026-12-31.
Johnson Matthey (2500123383), 2022-01-01 -- 2026-12-31.
Volvo Group (PO:2435702-000), 2022-01-01 -- 2026-12-31.
Ultraeffektiva DeNOx-katalysatorer för biobränsle och hybriddrift
Swedish Energy Agency (2020-014116), 2020-11-16 -- 2024-12-31.
Infrared spectroscopy in time and space
Swedish Research Council (VR) (2019-05528), 2020-01-01 -- 2023-12-31.
Driving Forces
Sustainable development
Subject Categories (SSIF 2025)
Chemical Sciences
Materials Engineering
Chemical Engineering
Infrastructure
Chalmers Materials Analysis Laboratory
Areas of Advance
Materials Science
ISBN
978-91-8103-278-9
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5736
Publisher
Chalmers
KB-salen, Kemigården 4, Chalmers.
Opponent: Dr. Davide Ferri, Paul Scherrer Institute (PSI), ETH Zurich, Switzerland.